1. Field of the Invention
This invention relates generally to touchpads. More specifically, the present invention is a method of preventing accidental contact with a touchpad to be interpreted as intended data input, such as when the palm of a hand accidentally rests on a portion of the touchpad when performing other tasks such as typing on a keyboard or moving a touchstick pointer, trackball or mouse.
2. Description of Related Art
There are several designs for capacitance sensitive touchpads. One of the existing touchpad designs that can be modified to work with the present invention is a touchpad made CIRQUE® Corporation. Accordingly, it is useful to examine the underlying technology to better understand how any capacitance sensitive touchpad can be modified to work with the present invention.
The CIRQU® Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated as a block diagram in FIG. 1. In this touchpad 10, a grid of X (12) and Y (14) electrodes and a sense electrode 16 is used to define the touch-sensitive area 18 of the touchpad. Typically, the touchpad 10 is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these X (12) and Y (14) (or row and column) electrodes is a single sense electrode 16. All position measurements are made through the sense electrode 16.
The CIRQUE® Corporation touchpad 10 measures an imbalance in electrical charge on the sense line 16. When no pointing object is on or in proximity to the touchpad 10, the touchpad circuitry 20 is in a balanced state, and there is no charge imbalance on the sense line 16. When a pointing object creates imbalance because of capacitive coupling when the object approaches or touches a touch surface (the sensing area 18 of the touchpad 10), a change in capacitance occurs on the electrodes 12, 14. What is measured is the change in capacitance, but not the absolute capacitance value on the electrodes 12, 14. The touchpad 10 determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line 16 to reestablish or regain balance of charge on the sense line.
The system above is utilized to determine the position of a finger on or in proximity to a touchpad 10 as follows. This example describes row electrodes 12, and is repeated in the same manner for the column electrodes 14. The values obtained from the row and column electrode measurements determine an intersection which is the centroid of the pointing object on or in proximity to the touchpad 10.
In the first step, a first set of row electrodes 12 are driven with a first signal from P, N generator 22, and a different but adjacent second set of row electrodes are driven with a second signal from the P, N generator. The touchpad circuitry 20 obtains a value from the sense line 16 using a mutual capacitance measuring device 26 that indicates which row electrode is closest to the pointing object. However, the touchpad circuitry 20 under the control of some microcontroller 28 cannot yet determine on which side of the row electrode the pointing object is located, nor can the touchpad circuitry 20 determine just how far the pointing object is located away from the electrode. Thus, the system shifts by one electrode the group of electrodes 12 to be driven. In other words, the electrode on one side of the group is added, while the electrode on the opposite side of the group is no longer driven. The new group is then driven by the P, N generator 22 and a second measurement of the sense line 16 is taken.
From these two measurements, it is possible to determine on which side of the row electrode the pointing object is located, and how far away. Pointing object position determination is then performed by using an equation that compares the magnitude of the two signals measured.
The sensitivity or resolution of the CIRQUE® Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of 960 counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes 12, 14 on the same rows and columns, and other factors that are not material to the present invention.
The process above is repeated for the Y or column electrodes 14 using a P, N generator 24
Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes 12, 14 and a separate and single sense electrode 16, the sense electrode can actually be the X or Y electrodes 12, 14 by using multiplexing. Either design will, enable the present invention to function.
It should be understood that a touchpad is defined as a touch sensitive surface, thus any touch sensitive surface such as a touchscreens should be considered to fall within the scope of the present invention. Accordingly, any touch sensitive surface will be referred to hereinafter as a touchpad, but should be considered to include any type of touch sensitive surface using any type of touch input technology, and should not be considered to be limited to mutual capacitance technology.
Using a touchpad in certain environments can be difficult because of the location of a touchpad within a computing device. For example, in a laptop or other portable computing device, a touchpad is often placed just in front of a keyboard. When a user is typing, the thumb or the palm of the hand just below the thumb can easily brush against a portion of the touchpad. This inadvertent contact with the touchpad can be misinterpreted as intentional input to the portable computing device. Unintended data input includes deselecting an item such as an icon shown on a graphical user interface, a mouse button click, or movement of the cursor. Accidental mouse button clicks are especially inconvenient because they may result in unwanted repositioning of a text insertion point, which can cause typed text to appear in the wrong place.
To remedy this problem, some software drivers for touchpads implement a feature where all input from the touchpad is inhibited while keystrokes are being detected. When a certain time interval (timeout) has elapsed after the last detected keystroke, input resumes.
The solution described above of using a timeout interval has a problem. If the timeout interval is too short, unwanted input from a touchpad can still occur if the user pauses for a short time while typing and then brushes against the touchpad before resuming typing. In addition, if the timeout interval is too long, then the user has to wait for an inconveniently long period of time before being able to resume touchpad input.
Another problem associated with unintended touchpad input is that the timeout solution is typically provided in the driver software. However, if a customized touchpad driver is not available or installed, then the ability of the touchpad to avoid unintended input is prevented or limited.
Accordingly, it would be an improvement over the prior art to provide a system and method for preventing unintended touchpad input caused by accidental contact with a touchpad surface by a palm, thumb or finger. It would be a further improvement to provide such improvements to touchpad performance regardless of whether or not a software driver is installed or available.